Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

89Administering disks
Placing disks under VxVM control
Adding foreign devices
DDL may not be able to discover some devices that are controlled by third-party drivers,
such as those that provide multipathing or RAM disk capabilities. For these devices it may
be preferable to use the multipathing capability that is provided by the third-party drivers
for some arrays rather than using the Dynamic Multipathing (DMP) feature. Such foreign
devices can be made available as simple disks to VxVM by using the
vxddladm
addforeign command. This also has the effect of bypassing DMP for handling I/O. The
following example shows how to add entries for block and character devices in the
specified directories:
# vxddladm addforeign blockdir=/dev/foo/dsk \
chardir=/dev/foo/rdsk
By default, this command suppresses any entries for matching devices in the OS-
maintained device tree that are found by the autodiscovery mechanism. You can override
this behavior by using the
-f and -n options as described on the vxddladm(1M) manual
page.
After adding entries for the foreign devices, use either the vxdisk scandisks or the
vxdctl enable command to discover the devices as simple disks. These disks then
behave in the same way as autoconfigured disks.
The foreign device mechanism was introduced in VxVM 4.0 to support non-standard
devices such as RAM disks, some solid state disks, and pseudo-devices such as EMC
PowerPath. This mechanism has a number of limitations:
■ A foreign device is always considered as simple disk with a single path. Unlike an
autodiscovered disk, it does not have a DMP node.
■ It is not supported for shared disk groups in a clustered environment. Only standalone
host systems are supported.
■ It is not supported for Persistent Group Reservation (PGR) operations.
■ It is not under the control of DMP, so enabling of a failed disk cannot be automatic,
and DMP administrative commands are not applicable.
■ Enclosure information is not available to VxVM. This can reduce the availability of
any disk groups that are created using such devices.
If a suitable ASL is available for an array, these limitations are removed, as described in
“Third-party driver coexistence” on page 83.
Placing disks under VxVM control
When you add a disk to a system that is running VxVM, you need to put the disk under
VxVM control so that VxVM can control the space allocation on the disk. Unless you
specify a disk group, VxVM places new disks in a default disk group according to the
rules given in “Rules for determining the default disk group” on page 160.